Charge coupled devices, CCDs, have application both to storage of signals, i.e., memories, and in detection of light information, i.e., image arrays. CCDs have been utilized both in random access memories and also in scanning arrays for both television pictures and line scanners.
However, an important characteristic of a charge coupled device is the efficiency at which the charge is transferred from one stage to another. In an article in the IEEE Transactions on Electron Devices, Volume ED-22, number 2, February 1975, Page 40, entitled "Experimental Characterization of Transfer Efficiency In Charge-Coupled Devices", there is disclosed a method of determining the minimum fat zero which eliminates fixed loss. In a book entitled "Charge Coupled Devices and Systems" by M. J. Howes and D. V. Morgan, John Wiley and Sons, copyrighted in 1979, on Page 179 thereof, is discussed that one of the levels of the binary signal in a CCD memory loop is a full well while the other level is an empty well. In practice, however, in order to assure a good transfer efficiency, the full well signal represents a charge signal that fills only about 80 percent to 90 percent of the potential well. Also, in the case of surface-channel CCDs, the "zero" signal usually represents some finite level of charge signal. This minimum level of charge signal required to reduce the charge trapping losses due to the fast interface states in the surface-channel CCDs, has been referred to as the "fat zero" signal.
According to the present invention, a high density quadrilinear CCD imaging array, in which a series of photosites absorb light and collect the electrons thereby generated, is disclosed wherein the electrons are transferred to an outer register passing through an inner register and thus are subject to a potential step created by two dimensional fringing fields. The inner registers and outer registers would each have an input diode, followed by two additional cells and an electron sink in order to serve as the drain of excess electrons from the cells in which the fat zero charge packets are created. When the full well of electrons is injected into the following cell, most of the electrons are bled off into the electron sink. Both of these extra cells would be structured identically to cells in the remainer of the CCD registers, with the exception that there are no photosites to supply charges.